While numerous randomized controlled clinical trials document the efficacy of nonsteroidal anti-inflammatory drugs (NSAIDs) in the symptomatic management of patients with OA, the utility of non-pharmacologic therapy (e.g., exercise, tidal lavage [TL]) has not been subjected to similar critical evaluation. Nonetheless, because of the increased awareness of the risks and costs of NSAID therapy, interest in alternative treatments of OA continues to grow. TL is being used increasingly to treat knee OA. However, even though the risks associated with the procedure appear to be small, charges for TL are as high as $800, while the efficacy of the procedure, duration of benefit, and which patients are most likely to benefit from TL are wholly unknown. This study has two major aims. The first is to evaluate the efficacy of TL, in comparison with placebo TL (sham lavage--SL) in relieving joint pain in patients with knee OA. Since subjects will be allowed to continue their usual arthritis therapy, which may or may not include an NSAID, the investigators hope to define the potency of TL and to assess it both as an adjunct to, and as an alternative for, NSAID therapy. All study subjects will meet American College of Rheumatology criteria for knee OA and will have current knee pain. Subjects with a broad spectrum of OA severity, as judged by knee radiography, will be included. The investigators will employ 2 treatment groups of approximately 120 patients each. One group will undergo TL, while the other group will undergo sham lavage. To meet their second major aim, which is to determine whether the duration of response to TL is clinically significant, they will follow subjects at 12-week intervals for 6 months, and again after one year, during which time differences between treatment groups will be examined. A third, but lesser, objective is to identify clinical, radiographic, laboratory, socioeconomic and/or general health status factors that might predict responsiveness to TL. Primary outcome measures will include the pain and physical function scales of the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC). The investigators will also evaluate the influence on clinical outcome after TL of the following: demographic and OA disease- specific characteristics, including baseline WOMAC score; radiographic severity of OA, synovial fluid leukocyte count and crystal content; and general health status, as measured by the Quality of Well Being (QWB) scale. Inclusion of the QWB will allow assessment of the cost-utility of TL. The investigators state that the results of this study will carry important implications for health policy decisions and reimbursement determinations.